Sets for extracorporeal blood handling, and also parenteral solution sets, generally require flow-through chambers, often called drip chambers, which, in use, utilize an upper liquid level of the medical liquid passing through it, with an air space on top. Such chambers generally have a permanently connected, branching, hollow-bore, flexible, branch line communicating with said air space for an air pressure line which connects via a reversible connector at its remote end to an equipment pressure port on the permanent equipment, which in turn communicates with a pressure monitor transducer for measuring air-pressure in the chamber as a surrogate for blood-pressure. A pressure-transmitting sterility barrier or diaphragm separates the sterile, disposable set and the unsterile permanent equipment.
These sets generally need to be initially primed with saline or another parenteral solution, where the proper upper liquid level is provided in each drip chamber present. Then, in the field of extracorporeal blood handling such as in hemodialysis, connection may be made with a fistula set or other means of access to the patient's bloodstream, and the saline in the primed set is replaced by blood, which is transferred to and from an extracorporeal blood processing device. These devices may comprise hemodialyzers, hemofilters and other devices for extracting components in the blood and returning the balance to the donor.
Alternately, it is also known for a flow-through chamber to incorporate a diaphragm as the pressure-transmitting sterile barrier which may be in direct contact with blood or another parenteral solution, or may only be in contact with air above the upper liquid level. For example, see Madsen et al. U.S. Pat. No. 3,713,341, Borsanyi U.S. Pat. No. 3,863,504, and Gangemi U.S. Pat. No. 4,077,882.
As taught in Brugger et al. U.S. Pat. No. 5,693,008, a flow-through chamber or “pod” is provided, having a diaphragm that transmits pressure but prevents passage of blood across said diaphragm. The pod comprises a rigid chamber in which said diaphragm is mounted and which further comprises a reversible connector which communicates with an airspace between said connector and the non-sterile side of said diaphragm. Said reversible connector, air space and non-sterile diaphragm side are open to atmosphere prior to medical treatment. To prepare for treatment, the reversible connector is connected directly to the pressure port on the face of the dialysis machine. Thus, a pressure tight system is attained and the machine's pressure transducer can measure pressure in the sterile set's flow-through blood pathway. Flow-through blood tubing must convey blood to and from that pod mounted on the face of the machine.
As a disadvantage of these diaphragmatic systems, the great majority of over 100,000+dialysis machines which are clinically used at the present time have their pre-pump arterial, post pump arterial and/or venous pressure ports for measuring blood pressure positioned on the face of the machine remote from other sites to which the blood tubing must be routed, such as the to the blood pump, the dialyzer (in the case of hemodialysis), the safety shut-off clamp, etc. Thus there is a disadvantage in the use of this system. It is always desirable to minimize the length of the extracorporeal blood flow path, both for reasons of simple economy, to minimize extracorporeal pressure drop and clottable surface area, as well as to minimize the total extracorporeal blood volume.
It is a further disadvantage of the current diaphragmatic system that the non-sterile side of the diaphragm is open to atmosphere prior to being brought into sealing relation with the equipment's pressure port, and therefore may be displaced prior to use. Such displacement results in pressure measurement errors and/or limited pressure measurements.
It is a disadvantage of sets which fit the great majority of the world's dialysis machines that they have drip chambers and permanently attached branch lines. Such branch lines complicate the sets' construction, packaging and use and are expensive.
By this invention, a generally airless pressure chamber (called a “pod”) which contains a diaphragm may be used as a substitute for a pressure monitoring drip chamber regardless of the front panel placement of necessary equipment. By this invention the pod is not connected to the pressure port on the face of a dialysis machine, but is spaced therefrom, and the important function of pressure monitoring still takes place. This achieves numerous advantages when compared with the prior drip chamber. Specifically, in the pod of this invention, it becomes unnecessary to set a liquid level as in many prior art chambers, and a blood-air interface can be completely avoided. At the same time, the chamber of this invention may be significantly smaller than the drip chambers of the prior art, and thus may have a reduced priming volume. Also, the volume of the chamber can be temporarily further reduced by manipulation of the diaphragm, for example during the rinse back step in extracorporeal blood handling procedures such as dialysis, to reduce the amount of solution needed in the rinse back process.
Also by this invention there are achieved important advantages when compared with the pods of the prior art. Compared with the priming volume and tubing costs of extracorporeal circuits using pods of the prior art, this invention saves cost because less large-bore blood tubing, but more small bore air pressure monitoring tubing, is used, the latter not containing blood. Thus it can be of a much finer, and cheaper, gauge than blood tubing, resulting in a net savings of plastic and cost, with less blood volume.
Sets utilizing the pod of this invention are easier to prime and operate, because there is no liquid level needed to be set in a chamber, as in the prior art. The pod of this invention may have branch connections for access to parenteral solutions such as saline or heparin solution, and it also may carry a connected, blood-free pressure monitor line (pressure tubing) for connection to a remote pressure port, for the monitoring of particularly blood pressure in the tubular set which carries the chamber. Cost may be saved in the manufacture and assembly of the set of this invention, since the blood tubing may be shortened, as it does not have to extend to the face of the dialysis machine, while also reducing extracorporeal blood volume (priming volume), as a clinical advantage.
The pod of this invention may be positioned precisely where pressure needs to be determined. For example, to detect line kinks or leaks, the pressure measuring chamber or pod should be upstream of the tubing which may leak or become kinked. Where a dialyzer is remotely monitored from a machine (as is generally the case) the placing of a pressure measuring chamber or pod immediately downstream from it is impossible in the case of drip chambers or prior art pods. As a further advantage, the pressure chamber of this invention does not require a permanently connected pressure monitor line. Rather, it can connect with a reusable pressure monitor line. Thus the set utilizing the chamber is less expensive, and there is an overall saving of cash because many disposable sets may be sequentially used with a single pressure monitor line, if desired.